I have to say that these are amazing value. I bought a pair for myself and another for my travelling companion before a recent long haul flight. For the first time ever the inflight entertainment was worthwhile. Likewise, my laptop (with a double headphone adaptor) was an invaluable companion. Previously, I had never bothered with either when flying since I found that no matter what the headphones were that the sound was always drowned out by the constant roaring, whining, hissing and the rest.
There's more to the noise cancelling than just in flight entertainment, though. Just turn these on with nothing connected and a 747 was suddenly an environment in which I could actually fall asleep for the first time ever. So much so that taking them off again was a bit of a shock!
Outside of this they are actually very good headphones that would be worth the money at the price in themselves. Moreover, they are oddly even better with the cancelling turned on even in a quiet room. Somehow anything becomes more engaging and enveloping when you do turn it on.